Bifidobacteria are widely known as one of the useful group of intestinal bacteria, and a multitude of publications exist relating to the physiological significance of this group of bacteria. For example, it has become clear that bifidobacteria produce organic acids such as lactic acid and acetic acid within the intestine, and also have effects in terms of suppressing the multiplication of harmful bacteria, producing vitamins, and activating immunity and the like.
For this reason, various preparations containing live bifidobacterial cells have been proposed in the past (Non-Patent Document 1). In addition, for the purpose of maintaining good health through the ingestion of bifidobacteria, various food products have been developed that contain bifidobacteria, such as fermented milk products including yogurts, sweets, drinks, and health foods. Furthermore, infants who are fed with breast milk during their infancy and early childhood tend to have superior levels of bifidobacteria, and therefore products such as powdered milk for infants or children containing bifidobacteria and/or lactic acid bacteria are also being developed in countries outside Japan. Currently, the longum species are mainly added as bifidobacterial species to food products in the world market, and there are also some products which use the breve species in combination (Non-Patent Document 2).
It is thought that individual display of the viable count for useful bacteria added in the products is beneficial for consumers in terms of providing as much information on the products as possible. In addition, with respect to the display of viable cell counts, the law has been established in Indonesia to display the viable cell count for each useful bacterial species added to the products.
Currently, as a method for determining the viable cell count for either one of the bacterial species in the products containing both bifidobacteria and lactic acid bacteria, a method to use a culture medium in which only bifidobacteria grow or a method to culture lactic acid bacteria alone through aerobic cultivation has already been established.
In addition, as a method for identifying the species of bifidobacteria in the products containing several species of bifidobacteria or lactic acid bacteria and also determining the viable cell count thereof, there is a method in which they are determined either from the morphology (i.e., color, shape, or the like) of colonies formed anaerobically or from the morphology of bacteria through Gram staining, by growing bacteria smeared on a culture medium that is prepared by adding sterile defibrinated blood to a BL agar medium (Non-Patent Document 3).